1. Field of the Invention
The present invention relates to an arrangement for fastening a covering on an printing unit cylinder of a printing press. The covering can, for instance, be a flexible printing plate or a rubber-blanket unit consisting of a flexible support plate and a rubber coating.
2. Description of the Prior Art
German reference DE 295 07 523 U1 shows a device for fastening a rubber-blanket unit on a blanket cylinder. In accordance therewith, the bent-over flanges of the support plate for the rubber blanket are inserted into a narrow slot in the cylinder. In its lower region, the slot is tangent to a longitudinal bore in the cylinder within which there is a clamping spindle which contains radially resilient rams. By a suitable turning of the clamping spindle, the rams are directed against the flanges of the support plate and press them against one wall of the slot. The device, to be sure, has a narrow clamping channel, but it is difficult to manufacture. Thus, upon penetration through the slot and the bore of the blanket cylinder, tapered end regions of material are produced which are forced away by the machine tool and must subsequently be removed, at great effort, by hand since they have a disturbing effect on the rotation of the spindle. Furthermore, the narrow milling tool can be forced away and damaged. Still further, the entrance edges of the slot must be rounded with different radius millers (acute and obtuse guide flanges). The device additionally requires long flanges of the support plate, which impedes their insertion into and removal from the slot. Furthermore, long flanges are, by their nature, not easy to handle in view of their slight stiffness. Long flanges are also difficult to slide into the slot when the blanket cylinder is rolled over in contact with other cylinders, since the tendency to form kinks increases quadratically with the length of the flanges. Finally, the flanges are not loaded uniformly by the resilient rams over their length.
WO 93/09952 also shows the fastening of a rubber-blanket unit on a blanket cylinder. Here, a clamping slot is provided, on the edge of which the leading flange of the support is hooked. The trailing flange is pressed in the bottom of the slot by a cam against a wall of the slot. This flange is again very long and has the disadvantages already described above. Furthermore, the cam fastening holds the trailing flange of the support firm in a non-displaceable manner, so that subsequent shifting, i.e. subsequent clamping when the blanket cylinder is rolled over, is not possible.
A device for fastening a printing plate on a form cylinder is shown in European reference EP 0 534 579 A2. The form cylinder has a cylinder groove extending in axial direction, within which there is a swingable clamping spindle. The spindle bears U-shaped leaf springs. One flange of the leaf springs presses the leading flange of the plate against a wall of the groove while the second spring arm is bent and engages into an angular bend of the trailing flange of the plate. In order to be able to contain and swing both spring arms, a correspondingly wide clamping channel is necessary. A greater width of the channel is also necessary in order to be able to introduce the trailing flange of the plate with its bend into the cylinder groove. A wide channel produces large vibrations in the printing unit and causes correspondingly wide non-printable stripes on the web.